Superconductivity in sulfur-doped amorphous carbon films

Following our previous investigations on superconductivity in amorphous carbon (aC) based systems; we have prepared thin composite aC-W films using electron-beam induced deposition. The films did not show any sign for superconductivity above 5 K. However, local, nonpercolative, superconductivity emerged at T _c=34.4 K after treatment with sulfur at 250 C for 24 hours. The superconducting features in the magnetization curves were by far sharper compared to our previous results, and the shielding fraction increased by about an order of magnitude. Our data suggest that pairing and localized superconductivity take place in the aC-S regions, whereas phase coherence, assisted by the W inclusions, was enhanced compared to our previous samples, yet still not to the degree of achieving global phase-coherence and percolating superconductivity.